1. Field of the Invention
The present invention relates to a defect inspection apparatus and a defect inspection method suitable for inspection of scratches, dust, and other defects present in a pattern formed in films in a process of manufacture of a semiconductor device having for example a stacked film structure.
2. Description of the Related Art
Up to the present, inspection of scratches present in a pattern on a semiconductor wafer, dust adhering to the pattern, and other defects in the process of manufacture of a semiconductor device has been carried out by taking the image of the semiconductor wafer creating a contrast waveform from the two dimensional image and detecting the same.
FIG. 5 is a view schematically showing principal parts of an example of the configuration of a defect inspection apparatus for inspection of scratches present in a pattern on a semiconductor wafer, dust adhering to the pattern, and other defects.
The defect inspection apparatus shown in FIG. 5 is configured so as to emit a beam of visible light from a lamp 101 via a lens 102, a half mirror 103, and an object lens 104 onto a semiconductor wafer W and to receive the beam of reflected light via the object lens 104, the half mirror 103, and an image-forming lens 105 at a camera 106.
In the defect inspection apparatus having the above configuration, the beam of light reflected from the semiconductor wafer W passes through the object lens 104, half mirror 103, and image-forming lens 105 to be received at the camera 106, a contrast waveform reflecting the surface shape of the semiconductor wafer W is created based on an intensity of the light received by the camera 106, and the defect present in a pattern formed on the semiconductor wafer W is detected from this contrast waveform by the naked eye or the like.
FIG. 6A is a sectional view in the process of manufacture of a semiconductor device having the stacked film structure as an object to be inspected by the defect inspection apparatus, while FIG. 6B is an example of the contrast waveform of the surface shape of the semiconductor device shown in FIG. 6A by the defect inspection apparatus.
In the structure of the semiconductor device shown in FIG. 6A, for example, a silicon oxide pattern SP is formed on the wafer W, and an aluminum interconnection pattern AP is formed on this silicon oxide pattern SP.
As will be understood from FIGS. 6A and 6B, the contrast waveform at a step difference between the resist pattern RP and the aluminum interconnection pattern AP has a different shape from the actual shape due to the coverage of the aluminum.
Summarizing the problem to be solved by the invention, the shape of the step difference present between the resist pattern RP and the aluminum interconnection pattern AP cannot be accurately determined from a region PA and a region Pr of the contrast waveform obtained by the defect inspection apparatus.
In the defect inspection apparatus, when there is a relatively deep and inclined step difference in the pattern like the inclined surfaces of the resist pattern RP and the aluminum interconnection pattern AP, there is a disadvantage that even if there is for example a scratch, adhesion of dust, or another defect in these inclined surfaces, it cannot be detected.
In the related art, when there is a relatively deep and inclined step as described above in the pattern stacked on the semiconductor wafer, for example a scanning electron microscope (SEM) has been used to conduct a sampling inspection from among a large number of semiconductor wafers.
In defect inspection using a scanning electron microscope, however, the number of the scanning electron microscopes which can be introduced is limited from the viewpoint of the plant and apparatus investment since scanning electron microscopes are high in cost. Further, the number of the semiconductor wafers inspected is limited since the throughput of the inspection is low.
Semiconductor wafers not inspected for defects are sent to the next step. These uninspected semiconductor wafers have become a cause of reduction of the yield of the product.
In the future, in the process of manufacture of a semiconductor device, along with the miniaturization of the circuit pattern of integrated circuits, employment of a stacked film structure of more layers for the semiconductor device cannot be avoided, so development of a defect inspection apparatus which can correctly inspect minute defects existing in a semiconductor wafer in the process of manufacture of a semiconductor device at a low cost and with a high throughput has become necessary.
An object of the present invention is to provide a defect inspection apparatus and a defect inspection method capable of more reliably and quickly detecting defects existing in patterns formed in the stacked films formed on a wafer in for example a process of manufacture of a semiconductor device, more particularly capable of reliably and quickly detecting minute defects even if there are step differences and other unevenness at the surface of the wafer.
According to a first aspect of the present invention, there is provide a defect inspection apparatus for inspecting for a defect existing in a inspected surface, comprising a light source for emitting a beam of light of a predetermined frequency band, a light frequency changing means for receiving as its input the beam of light emitted from the light source and outputting the related beam of light converted to a plurality of beams of inspection light having close frequencies different from each other and a beam of reference light beam, a light focusing means upon which the beams of inspection light output from the light frequency changing means are incident through an identical optical path and focusing the related beams of inspection light to the inspected surface to forming a plurality of different focal points corresponding to the beams of inspection light, a scanning means for scanning the focused beams of inspection light on the inspected surface, a superposing means for superposing the beam of the reflected light of the inspection light from the inspected surface and the beam of reference light to cause interference between the beams of reflected light and the beam of reference light, a light receiving means upon which the superposed light of the beams of reflected light and the beam of reference light is incident and detecting the intensity of the superposed light by confocal detection, and a contrast waveform generating means for generating contrast waveforms in the scanning direction at the focal positions in respect to the light intensity detected by the light receiving means and combining the contrast waveforms.
Preferably, the apparatus further comprises a defect detecting means for detecting defects of the pattern based on the contrast waveforms.
Preferably, the light receiving means has a light receiving element for receiving the superposed light and a pin hole plate provided in an incident light path of the superposed light to the light receiving element and having a small aperture and detecting the intensity of the superposed light by confocal detection.
Preferably, the light source selectively output a beam of visible laser light of a visible band and a beam of far-ultraviolet laser light of a far-ultraviolet band.
Preferably, the superposing means has beam splitters for reflecting the beam of reference light output from the light frequency changing means to the light receiving means, passing the beams of reflected light from the inspected surface striking it after following an identical optical path as that for the beams of inspection light, and exposing the same to the light receiving means.
Preferably, the light frequency shifting means has a plurality of acousto-optic modulating means for changing the frequency of the light emitted from the light source by supersonic waves of different frequencies from each other.
Preferably, the inspected surface comprises uneven surface.
Preferably, the inspected surface comprises the surface of a film stacked on a semiconductor substrate and formed into a predetermined pattern.
More preferably, the patterns are formed symmetrical about a predetermined center line, and the defect detecting means detects a part which is not symmetrical about the center line in the contrast waveform data obtained by the contrast waveform generating means as a defect.
Preferably, the scanning means has a galvanomirror or a supersonic light polarization element for scanning the beams of inspection light on the inspected surface.
Preferably, the scanning means two-dimensionally scans the beams of inspection light on the inspected surface, and the contrast waveform generating means generates a contrast image reflecting a three-dimensional shape of the inspected surface from the combined contrast waveforms obtained as a result of the scannings.
According to a second aspect of the present invention, there is provided a defect inspection apparatus for inspecting for a defect present in an inspected surface, comprising a light source for emitting a beam of light of a predetermined frequency band, a light frequency changing means for receiving as its input the beam of light emitted from the light source and outputting the related beam of light converted to a plurality of beams of inspection light and a beam of reference light beam having close frequencies different from each other, a light focusing means upon which the beams of inspection light output from the light frequency changing means are incident through an identical optical path and focusing the related beams of inspection light to the inspected surface to form a plurality of different focal points corresponding to the beams of inspection light, a scanning means for making the focused beams of inspection light scan the inspected surface, a superposing means for superposing beams of reflected light of the beams of inspection light from the inspected surface and the beam of reference light on each other to cause interference between the related beams of reflected light and the beam of reference light, a light receiving means upon which the superposed light of the beams of reflected light and the beam of reference light is incident and detecting the intensity of the superposed light, a contrast waveform generating means for generating contrast waveforms in the scanning direction at the focal positions based on the light intensity detected by the light receiving means and combining the contrast waveforms, and a defect detecting means for detecting a defect of a pattern based on the contrast waveforms.
Preferably, the inspected surface comprises the surface of a film stacked on a semiconductor substrate and formed into a predetermined pattern.
Preferably, the patterns are formed symmetrical about a predetermined center line and the defect detecting means detects a part which is not symmetrical about the center line in the contrast waveform data obtained by the contrast waveform generating means as a defect.
According to a third aspect of the present invention, there is provided a defect inspection apparatus for inspecting for a defect present in an inspected surface, comprising a light source for emitting a beam of light of a predetermined frequency band, a light frequency changing means for receiving as its input the beam of light emitted from the light source and outputting the related beam of light converted to a plurality of beams of inspection light and a beam of reference light beam having close frequencies different from each other, a light focusing means for focusing the related beams of inspection light output from the light frequency changing means on the inspected surface to form focal points, a scanning means for scanning the focused beams of inspection light on the inspected surface, a superposing means for superposing the beam of reflected light of the beams of inspection light from the inspected surface and the beam of reference light on each other to cause interference between the beams of reflected light and the beam of reference light, a light receiving means upon which the superposed light of the beams of reflected light and the beam of reference light is incident and detecting the intensity of the superposed light by confocal detection, and a contrast waveform generating means for generating contrast waveforms in the scanning direction at the focal positions based on the light intensity detected by the light receiving means.
Preferably, the apparatus further comprises a defect detecting means for detecting defects of the pattern based on the contrast waveforms.
Preferably, the inspected surface comprises the surface of a film stacked on a semiconductor substrate and formed into a predetermined pattern.
More preferably, the patterns are formed symmetrical about a predetermined center line, and the defect detecting means detects a part which is not symmetrical about the center line in the contrast waveform data obtained by the contrast waveform generating means as a defect.
Preferably, the light receiving means has an aperture plate having a small aperture for detecting the intensity of the superposed light by confocal detection in the incident optical path of the superposed light.
According to a fourth aspect of the present invention, there is provided a defect inspection method for inspecting for a defect present in an inspected surface, comprising converting light of a predetermined frequency band to a plurality of beams of inspection light and a beam of reference light having close frequencies different from each other, passing the plurality of beams of inspection light through the identical optical path and focusing them on the inspected surface to form a plurality of different focal points corresponding to the beams of the inspection light and scanning them the inspected surface, superposing the beams of reflected light of the beams of inspection light from the inspected surface and the beam of reference light on each other to cause interference between them and detecting the intensity of the related superposed light at the confocal point, generating contrast waveforms in the scanning direction at the focal positions based on the detected light intensity, combining the contrast waveforms, and detecting a defect of the inspected surface based on the combined contrast waveform.
Preferably, the method in the light frequency changing step, a beam of far-ultraviolet laser light of the far-ultraviolet band is used as the beam of light of the predetermined frequency band.
Preferably, at least part of the inspected surface comprises the surface formed.
Preferably, the method further comprises a step of selecting and using light of a frequency band differing according to the type of the object to be inspected constituting the inspected surface for the light of the predetermined frequency band.
Alternatively, preferably, the method further comprises a step of selecting and using one of a beam of far-ultraviolet laser light of the far-ultraviolet band and a beam of visible laser light of the visible band for the light of the predetermined frequency band according to the type of the object to be inspected constituting the inspected surface.
More preferably, the method further comprises a step of using the beam of visible laser light for inspection of an inspected surface constituted by a material such as polycrystalline silicon having a relatively low spectral reflectance for light of a short wavelength and a step of using the beam of far-ultraviolet laser light for inspection of an inspected surface formed by a material having a relatively high spectral reflectance for light of a short wavelength.
Preferably, the inspected surface comprises the surface of a film stacked on a semiconductor substrate and formed into a predetermined pattern.
More preferably, the patterns are formed symmetrical about a predetermined center line, and a part which is not symmetrical about the center line in the combined contrast waveform data is detected as a defect.
Preferably, the method further comprises two-dimensionally making the beams of inspection light scan the inspected surface, generating a contrast image reflecting a three-dimensional shape of the inspected surface from the combined contrast waveforms obtained as a result of the scannings, and detecting a defect of the inspected surface based on the contrast image.
Preferably, the method further comprises two-dimensionally making the beams of inspection light scan the inspected surface, generating a contrast image reflecting a three-dimensional shape of the inspected surface from the combined contrast waveforms obtained as a result of the scannings, and detecting a defect of the inspected surface based on the contrast image.
According to a fifth aspect of the present invention, there is provided a defect inspection method for inspecting for a defect present in an inspected surface, comprising converting light of a predetermined frequency band to a beam of inspection light and a beam of reference light having close frequencies different from each other, focusing the beam of inspection light on the inspected surface to form a focal point and scanning it the inspected surface, superposing the beam of reflected light of the beam of inspection light from the inspected surface and the beam of reference light on each other to cause interference between them and detecting the intensity of the related superposed light by confocal detection, generating a contrast waveform in the scanning direction at the focal position based on the detected light intensity, and detecting a defect of the inspected surface based on the contrast waveform.
That is, in the present invention, light emitted from a light source is converted to a plurality of beams of inspection light and a beam of reference light having close frequencies different from each other by the light frequency changing means.
The plurality of beams of inspection light output from the light frequency changing means are focused on the inspected surface by the focusing means through the identical optical path. The focused beams of inspection light have frequencies different from each other, so a plurality of different focal points are formed with respect to the inspected surface. The focused beams of inspection light are made to scan the inspected surface by the scanning means, the beams of reflected light from the inspected surface are superposed on the beam of reference light by the superposing means, and a beat of the differential frequency is produced by the superimposition.
The beat of the differential frequency is detected by the light receiving means. The detection of the beat of the differential frequency generated by interference between these beams of inspection light and the beam of reference light is referred to as optical heterodyne detection. By the optical heterodyne detection, the contrast characteristic of the image to be obtained is improved, and an SIN ratio of the detection light is improved.
Further, when detecting the optical intensity by optical heterodyne detection, the light receiving means detects the intensity by confocal detection.
Confocal detection is a detection method for making the reflected light pass through a pinhole, slit, or other aperture and strike the light receiving surface of the light receiving means and detecting the intensity of part of a range including the center portion of the distribution of the intensity of the reflected light. The optical resolution is improved by the confocal detection, and the contrast characteristic of the obtained image is improved.
The intensity information of the reflected light obtained at the light receiving means by the optical heterodyne detection and the confocal detection includes intensity information of the reflected light obtained at a plurality of different focal positions, so the contrast waveform generating means generates contrast waveforms in the scanning direction at the focal positions and combines the generated contrast waveforms.
The combined contrast-waveform is a combination of contrast waveforms obtained at a plurality of different focal positions, therefore even if there is a certain degree of unevenness in a depth direction in the surface shape of the inspected surface, a shape faithfully reflecting the surface shape of the inspected surface is exhibited.
A defect present in the inspected surface can be detected by the difference of the surface shape of the specified inspected surface from an intended shape based on the combined contrast waveform.